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gun fit question


mrsitter
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Hi all,

Just been wondering about how stock length affects gun fit and point of aim...

I have a trap gun with a stock length which is 14 1/2" now I'm 6'4" and they are to short when I do the old rough guide of length of pull by placing the butt in the crease of your forearm and your trigger finger knuckle just wrapped around the trigger so I bought 1 of those leather shoe's that fit over the stock to get the correct length I also placed a couple of pieces of carpet in the shoe so it extends the total length by 35mm making it about 16", just shooting off on a tangent another way of measuring stock length is to measure the distance when mounted from your hand/thumb knuckle to your eye and I believe the 2" distance is about right and guess what, when I mount without the shoe the distance is about 40mm which aint far off, which measurement is the best guide.... Back to my main question on my trap gun without the shoe I can see about 4mm of rib from the top lever to the end bead which you can expect with a trap gun and with the shoe on I see the thickness of a pound coin about 2.5mm which I believe is about right for a sporter. So my question is do I have 2 setups with the same gun (shoe on & shoe off) or will the point of aim be the same with both setups because I'm looking down the same focal plane on the stock which has a consistant drop.

 

I think I need to find something better to do on a friday night I know!!!

Cheers

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Yeah, I've always understood it that the pound coin thickness is about right for sporting clays and I think a lot of it depends on what feels right, I like shooting dtl and also sporting clays and I have often wondered if the trap stock setup will hamper my sporting shooting slightly and I have toyed with the idea of lowering the comb to sporterize it more or does the extra stock length effectively lower the point of aim so all I need to do is get it lengthened, it must be fairly simple geometery but I never paid attention at school...

Edited by mrsitter
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Hi,

Sorry about this, but the "old rough guide" is a load of old squit (as they say in Norfolk). Gun fit is a combination of inter-related factors moulded together. The starting point for stock length is related to the length of your neck Other than that comment, as this is about clays, just hope clayman spots the topic.

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These amounts are negligible.

 

Just do the maths.

 

From your eye to the bead will be around 100mm (1 metre)

 

So, for every 1.mm your eye is higher, the gun shoots to centre of pattern at 20m (22yds,) 20mm higher, thats less than an inch.

 

So, to extrapolate this, if you are 2.5mm higher , and shoot to a long range on a pattern plate,, say 40m ( 45yds), the centre of pattern is still only 100mm or 4" higher. This is in a pattern that should be 750mm across (30").

 

Unless you are capable of controlling the centre of your pattern within 4" at 45yds, these differences are so small as to be of no consequence what-so-ever, so you should use the comb height and stock length that is most comfortable to you.

 

The old concept of fore-arm length for stock length is only the roughest of guides, and should really be disregarded. There are big guys with short arms, and little guys with ape like appendages!

 

A much better guide is the distance between your nose and the knuckle of you thumb. Assuming correct stance and mount, this distance should be 40 - 60mm ( 1.5" to 2.5". In general, shorter measure for gun down faster mounting, and a longer measure for gun up shooters who pre-mount ( ie trap shooters). This is usually judged by 2 or 3 fingers in the gap.

 

3mm or a £coin on the rib is correct for general sporting, lower is a gun fit or mount problem. Higher improves visibility and lowers off -eye take over and barrel ghosting problems, but lifts the pattern. This may be an advantage in driven game / targets and for rising targets, ie trap shooting.

 

However, as the maths shows, you have to lift the eye a great deal to make any significant difference to pattern placement.

 

Even if you eye was 1/2" high, ( 13mm), this is 10mm above the bead, and still only 200mm or 8" different on the centre of pattern at 20m.

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